Tetrapod
The superclass Tetrapoda (Ancient Greek τετραπόδηs tetrapodēs, "four-footed"), or the tetrapods /ˈtɛtrəpɒd/, comprises the first four-limbed vertebrates and their descendants, including the living and extinct amphibians, reptiles, mammals, birds, and some extinct fish. Tetrapods evolved from the lobe-finned fishes around 390 million years ago in the middle Devonian Period, with modern tetrapod groups having appeared by the late Devonian, 367.5 million years ago. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear, and are areas of active research and debate among palaeontologists at present.
While most species today are terrestrial, the first tetrapods were fully aquatic. Amphibians today generally remain semiaquatic, living the first stage of their lives as fish-like tadpoles. Amniotes evolved about 340 million years ago (crown amniotes 318 mya), and their descendants drove most amphibians to extinction. One population of amniotes diverged into lizards, dinosaurs, birds and their relatives, while another diverged into mammals and their extinct relatives. Several groups of tetrapods, such as the caecilians, snakes, cetaceans, sirenians, and moas have lost some or all of their limbs. In addition, many tetrapods have returned to partially aquatic or fully aquatic lives throughout the history of the group (modern examples of fully aquatic tetrapods include cetaceans and sirenians). The first returns to an aquatic lifestyle may have occurred as early as the Carboniferous Period, whereas other returns occurred as recently as the Cenozoic, as in cetaceans, pinnipeds, and several modern amphibians.
Tetrapod (structure)
In coastal engineering, a tetrapod is a tetrahedral concrete structure used as armour unit on breakwaters. A tetrapod's shape is designed to dissipate the force of incoming waves by allowing water to flow around rather than against it, and to reduce displacement by allowing a random distribution of tetrapods to mutually interlock.
Earlier barrier material used in breakwaters, such as boulders and conventional concrete blocks, tended to become dislodged over time by the force of the ocean constantly crashing against them. Tetrapods and similar structures are often numbered so any displacement that occurs can be monitored from photographs.
The unit was originally developed in 1950 by Laboratoire Dauphinois d'Hydraulique (now Sogreah) in Grenoble, France. They are no longer protected by a patent, and are widely used all over the world, produced by many contractors.
The tetrapod inspired many similar concrete structures for use in breakwaters, including the Modified Cube (U.S., 1959), the Stabit (U.K., 1961), the Akmon (Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod (Romania, 1969), the Seabee (Australia, 1978), the Accropode (France, 1981), the Hollow Cube (Germany, 1991), the A-jack (U.S., 1998), and the Xbloc (Netherlands, 2001), among others. In Japan, the word tetrapod is often used as a generic name for wave-dissipating blocks including other types and shapes.
Analogion
An analogion (Greek: Ἀναλόγιον) is a lectern or slanted stand on which icons or the Gospel Book are placed for veneration by the faithful in the Eastern Orthodox Church and Eastern Catholic Churches. It may also be used as a lectern to read from liturgical books during the divine services.
Design
The analogion is normally slanted slightly, to make it easier for the one standing in front of it to see the icon or book laid on it. The analogion may have four legs or only one in the center. It is often covered with rich cloth (antipendia) which either partially or completely covers the analogion on all sides. Some analogia are made so they fold for easy portability, some are intricately carved of fine wood, and some are simple framework intended to be completely covered with cloth. They are normally light enough to be moved without too much difficulty.
There is also a type of analogion which is used in the kliros by the chanters. This often has two or three sides and turns to allow the singers to more easily use the numerous liturgical texts required during the services.
Podcasts:
